Minimally invasive surgery (MIS) for the spine has established itself on the cutting edge for patients seeking surgical treatment of common spinal disorders with decreased peri-operative pain, reduced blood loss, shorter hospitalization, easier and shorter recovery, and, most importantly, equivalent long-term efficacy as compared to open surgical procedures.
MIS for the spine began with simple decompression procedures for lumbar disc herniations. Next, surgeons used MIS surgical techniques to perform decompressions for lumbar stenosis and cervical discectomies and decompressions. Subsequently, surgeons implanted spinal instrumentation using minimally invasive techniques. Now, a surgeon can accomplish the vast majority of commonly performed spinal surgeries using minimally invasive techniques.
Several MIS spinal surgeries approach the spine through the lamina of the vertebra by drilling, cutting away or totally removing the lamina bone. Surgeries such as cervical laminectomy, lumbar disectomy and lumbar laminectomy are examples where the procedure can be performed through the lamina, which results in a compromised lamina having a hole or gap. One common procedure that can be performed with MIS for the spine is lumbar laminectomy for stenosis.
FIG. 1 is a top view and FIG. 2 is a posterior view of a vertebra 10 including a vertebral body 12, a spinal canal 14 through which the spinal cord and nerves 20 travel, a spinous process 30, pedicles 18 on both sides of the spinous process 30, a neural foramina 36 adjacent to the pedicles 18 through which nerves that leave the canal 14 travel, a superior articular facet 26 on both sides of the spinous process 30 that are part of a facet complex joint including the superior facet 26 of the vertebra 10 and an inferior articular facet of an adjacent vertebra (not shown), an inferior articular facet 24 on both sides of the spinous process 30 that are part of a facet complex joint including the inferior facet 24 of the vertebra 10 and a superior articular facet of an adjacent vertebra (not shown), a transverse process 22 on both sides of the spinous process 30, a lamina 16 between the superior facet 26 and the spinous process 30 on both sides of the vertebra 10, and a ligamentum flavum 38 beneath the lamina 16.
The vertebra 10 has stenosis, where the lamina 16, facet complex and the ligamentum flavum 38 have enlarged and grown into the spinal canal 14 causing narrowing of the spinal canal 14 so that it is more triangular shaped instead of oval shaped, resulting in compression of the nerves 20. The bone growth of the lamina 16, facet complex and the ligamentum flavum 38 can occur because of various reasons including degradation of the facet joint and/or instability, where the facet joint contacts the superior articular facet 26 and the inferior articular facet from the next lower vertebra. The patient can experience pain and/or numbness from this narrowing of the spinal canal 14 because it contacts and pinches nerves.
In one surgical procedure to perform lumbar laminectomy for stenosis with MIS techniques, the surgeon makes an incision 1.5 cm lateral to the midline. The incision is placed directly over the disc with the stenosis. An 18 gauge spinal needle and lateral fluoroscopy identify the location of the stenosis. The surgeon cuts the fascia with a Bovey cautery, which helps to facilitate passage of a K-wire and subsequent muscle dilators. The surgeon docks the K-wire on the laminar facet junction followed by an initial muscle dilator, and then removes the K-wire. The surgeon then slips increasingly larger muscle dilators over the preceding muscle dilators. Finally, the surgeon places a tubular retractor or an expandable MIS retractor over the stack of dilators. Access to the vertebra 10 is achieved when the surgeon removes all of the dilators leaving the tubular retractor. At this point the surgeon can bring a microscope into the operative field. Palpation of the facet complex lateral can be preformed and the “drop off” point between the facet and the laminar-facet junction can be palpated with the Bovey tip. The tubular retractor should be positioned to rest on the facet, but allow the ipsilateral lamina to be easy viewed. If needed, an antero-posterior fluoroscopic view can be preformed to confirm the retractor location.
The surgeon manipulates a drill tip through the tubular retractor to remove a portion of the lamina 16, leaving behind a hole or open area 34 in the lamina 16 defined by the removed lamina bone. A skilled surgeon can decompress both sides of the vertebra 10 by choosing an angular entry to have the drill access and undercut the contralateral lamina. Once adequate decompression has been achieved, the tubular retractor is removed allowing the paraspinal muscles to return to their normal anatomical location. The surgeon sutures the subcutaneous tissues and closes the skin with an adhesive.
FIG. 3 is a cross-sectional view and FIG. 4 is a posterior view of the vertebra 10 showing the open area 34 resulting from the removed lamina bone including both the ipsilateral lamina bone and the contralateral lamina bone that has been removed by undercutting the spinous process 30 and contralateral lamina with a drill. Note that the spinal canal 14 is no longer narrowed, or triangular shaped, but has been restored to the more appropriate oval shape.
Although this procedure has left the spinous process 30 in place, and has restored the spinal canal 14, it still leaves the vertebra 10 structurally compromised, but where the spinous process 30 has been preserved including the muscle attachments to the spinous process 30. Particularly, the minimally invasive surgical technique for lumbar laminectomy for stenosis, and other surgeries, leaves the patient with a missing or damaged lamina 16. Also, in the case of laminectomy procedures, the remaining contralateral lamina may have been compromised by the undercutting of the lamina 16 to enlarge the spinal canal to relieve the pressure on the contralateral lamina side.
Bone graft material can be placed in the open area 34 where the lamina bone has been removed. However, the bone graft material can grow into the spinal canal 14. What is needed is a technique to replace the lost lamina bone that occurs during these types of surgical procedures while minimizing the risk that bone growth will encroach on the spinal canal.